An outdoor unit and a plurality of indoor units constituting an air conditioner mostly communicate with each other through wired communication such as RS-485 communication. In such wired communication, a communication line has to be additionally provided between the outdoor unit and the indoor units, and a pipe configured to protect the line has to be installed together with the communication line.
In addition, when re-installing the air conditioner by using an existing refrigerant pipe, the line cannot be reused and re-installed.
In order to solve such problems, there has been an attempt to replace RS-485 communication with a pipe communication scheme. However, when the RS-485 communication is replaced with the pipe communication scheme, there is an issue about how to make communication.
A research on a technique about an implementation method such as ensuring communication reliability and address allocation according to pipe communication has been conducted. However, in practice, a communication signal has to be increased in order to ensure a communication distance, and an air conditioner standard (electromagnetic compatibility standard; EMC standard) may not be satisfied when the communication signal is increased, so that there has been a limit in applying the above implementation method to actual long-distance pipe communication.